The present invention relates to methods for controlling the migration of particulates, such as proppant and formation sands, within a portion of a subterranean formation through the use of a low-viscosity aqueous tackifying composition.
Hydrocarbon wells are often located in subterranean zones that contain unconsolidated particulates that may migrate within the subterranean formation with the oil, gas, water, and/or other fluids produced by the wells. The presence of particulates, such as formation sand, in produced fluids is disadvantageous and undesirable in that the particulates may abrade pumping and other producing equipment and reduce the fluid production capabilities of the producing zones. Unconsolidated subterranean zones include those that contain loose particulates and those wherein the bonded particulates have insufficient bond strength to withstand the forces produced by the production of fluids through the zones.
One method of controlling particulates in unconsolidated formations involves placing a filtration bed containing gravel near the well bore in order to present a physical barrier to the transport of unconsolidated formation fines with the production of hydrocarbons. Typically, such so-called “gravel packing operations” involve the pumping and placement of a quantity of a desired particulate into the unconsolidated formation in an area adjacent to a well bore. One common type of gravel packing operation involves placing a sand control screen in the well bore and packing the annulus between the screen and the well bore with gravel of a specific size designed to prevent the passage of formation sand. The sand control screen is generally a filter assembly used to retain the gravel placed during gravel pack operation. A wide range of sizes and screen configurations are available to suit the characteristics of the gravel pack sand used. Similarly, a wide range of sizes of gravel is available to suit the characteristics of the unconsolidated or poorly consolidated particulates in the subterranean formation. The resulting structure presents a barrier to migrating sand from the formation while still permitting fluid flow. When installing the gravel pack, the gravel is carried to the annulus in the form of a slurry by mixing the gravel with a viscous transport fluid. Once the gravel is placed in the well bore, the viscosity of the transport fluid is reduced, and it is returned to the surface. Some gravel packing operations, commonly known as “high-rate water packing” operations, the transport fluid viscosity is somewhat lowered and yet the gravel remains in suspension because the treatment occurs at a substantially higher velocity. Gravel packs act, inter alia, to stabilize the formation while causing minimal impairment to well productivity. The gravel, inter alia, acts to prevent the particulates from occluding the screen or migrating with the produced fluids, and the screen, inter alia, acts to prevent the gravel from entering the production tubing. Such packs may be time consuming and expensive to install.
Another method used to control particulates in unconsolidated formations involves consolidating unconsolidated subterranean producing zones into hard, permeable masses by applying a resin composition to the unconsolidated particulates. Another, similar method involves placing a non-aqueous tackifying composition to the unconsolidated particulates in an effort to reduce the migration of particulates within the zone. Whereas a resin composition produces a hard mass, the use of a non-aqueous tackifying composition produces a more malleable consolidated zone.